Melting Machine Research Articles

A simulation study of local powder bed gas shielding in Selective Laser Sintering / Melting machines

In Selective Laser Sintering and Melting it is necessary to protect metal powder deposited on the powder bed from contact with atmospheric air, which may lead to oxidation and downgrading of the properties of the powder in the presence of high temperature that is necessary for achieving full or partial melting. Thus, the building chamber of commercially available SLS/SLM machines is fully isolated and filled with inert shielding gas which may need to be replenished before each build session thereby raising both machine building and consumables costs. In this paper, it is examined using Computational Fluid Dynamics how protection of the powder area around the laser spot can be achieved by locally insulating it from air by gas circulation in a suitably designed box moving with the laser beam. Full coverage of the respective area and at the same time no disturbance of the powder particles within it are critical requirements. Two concept variants are studied and simulated with promising results.

Optimal process characteristics of melting of polyisoprene

Abstract The present problem in rubber industries are melting and processing of polymers and rubbers. The multi-axle melting machine is used to rectify the melting of these materials. In this paper, the polyisoprene is melted in multi-axle melting machine without slag pollution. The melting rate and its processing time also better than other melting method. The melting is brought uniform and its control the chemical composition. Mooney viscosity was determined based on the input factors. Thermocouple, sensor and controller were used to improve the melting process. The melting process parameters are optimized through taguchi optimization method and their parametric effects have been studied through variance analysis.

Analysis on Defocusing and Astigmatism of Electron Beam Selective Melting Machines

Affected by defocusing and astigmatism, the quality of electron beam steadily deteriorated with increasing deflection distance, limiting the processing area of SEBM machines. The relationship among beam spot size, deflection distance and deflection direction are studied by numerical simulation, which explains the cause of decreasing power density. The experimental results show that defocus is the main factor affecting the beam spot size when the deflection distance is less than 100 mm and astigmatism is the main factor at a larger deflection distance. Then, the chessboard electron imaging experiment is carried out to verify that the spot size increases with the deflection distance. Thus, dynamic focusing and astigmatism should be introduced at the same time to minimize beam area.

Microstructural Alteration of Alloyed Steel in Direct Metal Laser Melting by Powder Bed Deposition System

Herein, the microstructural alteration of alloyed steel by variation in process parameters is investigated using a powder bed deposition technology commonly available in industry as a direct metal laser melting (DMLM) machine. Two sets of process parameters with high heat and low heat inputs are used to print the specimens. Results show that modifications in the microstructure as a function of process parameters and exposured region shape. Electron back scatter diffraction data confirm that commonly observed epitaxial growth and strong {001} texture in additive manufactured steels can be removed using different set‐ups of process parameters.

Design and additive manufacturing of porous titanium scaffolds for optimum cell viability in bone tissue engineering

Pore size, external shape, and internal complexity of additively manufactured porous titanium scaffolds are three primary determinants of cell viability and structural strength of scaffolds in bone tissue engineering. To obtain an optimal design with the combination of all three determinants, four scaffolds each with a unique topology (external geometry and internal structure) were designed and varied the pore sizes of each scaffold 3 times. For each topology, scaffolds with pore sizes of 300, 400, and 500 µm were designed. All designed scaffolds were additively manufactured in material Ti6Al4V by the direct metal laser melting machine. Compression test was conducted on the scaffolds to assure meeting minimum compressive strength of human bone. The effects of pore size and topology on the cell viability of the scaffolds were analyzed. The 12 scaffolds were ultrasonically cleaned and seeded with NIH3T3 cells. Each scaffold was seeded with 1 million cells. After 32 days of culturing, the cells were fixed for their three-dimensional architecture preservation and to obtain scanning electron microscope images.

The Effect of Post-Processing on the Mechanical Behavior of Ti6Al4V Manufactured by Electron Beam Powder Bed Fusion for General Aviation Primary Structural Applications

In this work a mechanical characterization of Ti6Al4V processed by electron beam powder bed fusion additive manufacturing was carried out to investigate the viability of this technology for the manufacturing of flyable parts for general aviation aircraft. Tests were performed on different manufacturing conditions in order to investigate the effect of post processing as machining on the mechanical behavior. The study provides useful information to airframe designers and manufacturing specialists that work with this technology. The investigation confirms the low process variability and provides data to be used in the design loop of general aviation primary structural elements. The test results show a high level of repeatability indicating that the process is well controlled and reliable enough to match the airworthiness requirements. In addition, the so-called “as-built specimens”, i.e., specimens produced by the electron beam melting machine without any major post-processing, have lower mechanical performances than specimens subjected to a machining phase after the electron beam melting process. Specific primary structural elements will be designed and flight cleared, resulting from the findings presented herein.

Axial fatigue behaviour of additively manufactured tool steels

Tool steels contain high-nickel and low-carbon content, consisting of alloying elements such as Ni, Co, Mo, Ti and Al. These tool steels exhibit excellent mecahnical properties combining high strength with good toughness. The aim was to study the systematic series of tests in relation to recommended practice for plain strain fracture toughness measurements and fatigue strength using bending and axial fatigue testing to provide better insight insight into the processes controlling fatigue failure at all lives is gained. The fatigue specimen were produced using Selective Laser Melting Machine, with parameters that were chosen for production of test parts which result in highest density. The samples were sectioned and machined for further analyses which included, microstructure, tensile and fatigue testing. There is also evidence of martensitic needles structures observed on the top surface of the build plane is coherent and formed elongated grains. The ultimate yield strength of M300 Tool Steel showed almost 100% increase from 1100 MPa in the as built condition, up to 2050 MPa following heat treatment. The fatigue samples experience strain hardening and broke without significant plastic deformation as experienced during static tensile tests. The importance of heat treatment is evident in achieving improved fatigue life of tool steels.

Effect of single and multiple parts manufacturing on temperature-induced residual stress problems in SLM

In this study, the effects of the single and multiple productions of samples by additive manufacturing on residual stress and displacement (distortions) were investigated. The samples were manufactured by Selective Laser Melting (SLM) machine using Ti6Al4V powders. Each time a different number (1, 5 and 13 samples) of cubic shaped samples were produced on the building platform. During the process, samples were observed with a thermal camera first, in order to understand the relationship amongst the residual stress, displacement and temperature gradients. Then, displacement values were measured experimentally with Coordinate Measurement Machine (CMM) device. Next, both displacement and residual stresses were calculated via Finite Element Analysis (FEA) method. Finally, residual stresses and displacement equations were determined by genetic expressional programming (GEP) using the results and data obtained from the tests and FEA. According to the results, the regression values of residual stress and displacement equation were found to be 0.96% and 0.88%, respectively. As the number of manufactured samples on the same platform increased, temperatures and irregular temperature distribution were increased.

Development of an Additive Manufactured Artifact to Characterize Unfused Powder Using Computed Tomography

Additive manufacturing (AM) is recognized as a core technology for producing high-value components. The production of complex and individually modified components, as well as prototypes, gives additive manufacturing a substantial advantage over conventional subtractive machining. For most industries, some of the current barriers to implementing AM include the lack of build repeatability and a deficit of quality assurance standards. The mechanical properties of the components depend critically on the density achieved. Therefore, defect/porosity analysis must be carried out to verify the components’ integrity and viability. In parts produced using AM, the detection of unfused powder using computed tomography is challenging because the detection relies on differences in density. This study presents an optimized methodology for differentiating between unfused powder and voids in additive manufactured components, using computed tomography. Detecting the unfused powder requires detecting the cavities between particles. Previous studies have found that the detection of unfused powder requires a voxel size that is as small as 4 μm3. For most applications, scanning using a small voxel size is not reasonable because of the part size, long scan time, and data analysis. In this study, different voxel sizes are used to compare the time required for scanning, and the data analysis showing the impact of voxel size on the detection of micro defects. The powder used was Ti6Al4V, which has a grain size of 45–100 μm, and is typically employed by Arcam electron beam melting (EBM) machines. The artifact consisted of a 6 mm round bar with designed internal features ranging from 50 μm to 1400 μm and containing a mixture of voids and unfused powder. The diameter and depth of the defects were characterized using a focus variation microscope, after which they were scanned using a Nikon XTH225 industrial CT to measure the artifacts and characterize the internal features for defects/pores. To reduce the number of the process variables, the measurement parameters, such as filament current, acceleration voltage, and X-ray filtering material and thickness were kept constant. The VGStudio MAX 3.0 (Volume Graphics, Germany) software package was used for data processing, surface determination, and defects/porosity analysis. The main focus of this study is to explore the optimal methods for enhancing the detection of pores/defects while minimizing the time taken for scanning, data analysis, and determining the effects of noise on the analysis.

Post Processing of 3D Printed Metal Scaffolds: a Preliminary Study of Antimicrobial Efficiency

Additive manufacturing techniques enable users to produce complex devices that would not be possible by conventional methods, offering unique advantages to the medical industry due to the possibility to customize devices to accurately fit patient geometries. The process as done today needs still to be optimized in many aspects to achieve implants which better meet the requirements of the end application. Both the surface and the mechanical properties of the implant device have to better mimic the properties of the anatomical region of interest to assure a good interconnection with the surrounding tissue and the development of a strong interface. In the case of complex implants, the geometric accuracy of the replacing device is not the only factor with regard to the specific patient need. An optimal surface treatment after the manufacturing process can lead to a highly improved interaction of the implant with the surrounding physiological tissue. The improved outcome will be beneficial for the patient recovery process after the operation. This work goal is to provide an optimization of the post processing process of 3D printed titanium implants and the improvement of their performances, by a better and shorter assimilation of the implant to achieve the optimal patient wellness. In particular, the paper aims at the preliminary identification of the proper surface treatments that can lead to an implant that promotes the reduction of the bacterial adhesion to allow a better osseointegration in a long-term period. Ti6Al4V samples have been produced by a Selective Laser Melting (SLM) machine and the as-built surfaces have been treated in order to analyze the effects of post-processing on the surface and antimicrobial properties of the 3D printed specimens.

Non-Isothermal Crystallization Kinetics of a Rapidly Solidified as-Cast TiZrHfNiCu High Entropy Bulk Metallic Glass

This paper aims to investigate the thermal behavior and crystallization kinetics of TiZrHfNiCu high entropy bulk metallic glass (HE-BMG) alloy using the standard procedure of Differential Scanning Calorimetric (DSC) annealing technique. The alloy was produced using an arc melting machine with a critical diameter of 1.5 mm. The crystallization kinetics and phase transformation mechanism of TiZrHfNiCu HE-BMG was investigated under the isochronal condition at a single heating run based on the Johnson-Mehl- Avrami (JMA) theory. In isochronal heating, the apparent activation energy for glass transition and crystallization events was analyzed by Kissinger and Ozawa methods. The average activation energy value for crystallization of TiZrHfNiCu amorphous alloys in isochronal modes was 226.41 kJ/mol for the first crystallization and 297.72 kJ/mol for second crystallization stages. The crystallization mechanism of the first step was dominated by two- and three-dimensional growth with increasing nucleation rate, while the crystallization mechanism in the second stage was dominated by two-dimensional crystallization growth with a constant nucleation rate. The diffusion mechanism result proved the theory of sluggish atomic diffusion of HEA at elevated temperature.

Quality by Design for industry translation: Three‐dimensional risk assessment failure mode, effects, and criticality analysis for additively manufactured patient‐specific implants

AbstractThe complexity of patient‐specific implants combined with the current limited expertise in reliability engineering and manufacturability in the additive manufacturing (AM) sector is posing a number of quality performance challenges. Worldwide medical device regulatory bodies are facing increasing pressure to devise adequate standards to ensure long‐term patient safety and product performance. The implementation of the Quality by Design (QbD) system to titanium 3D‐printed bone implants offers a proven system to ensure that products are designed and manufactured correctly from the beginning without errors. This article reports on the development of a failure mode, effects, and criticality analysis (FMECA) coupled with a 3D risk assessment approach. This integrated approach is based on a questionnaire performed with three industry firms and three university research groups with significant experience and expertise in medical device product development and/or research in this field. Research outcomes include a FMECA form containing 137 failure modes with AM materials, AM machine general, fabrication, electron beam melting machine, finishing, and design being as the most sensitive process areas in terms of product quality. We subsequently propose corresponding preventive and corrective strategies for risk mitigation. The approach forms part of the QbD system being developed by the authors specifically for additive manufactured titanium patient‐specific implants.

Experimental and numerical study on residual stress and geometric distortion in powder bed fusion process

The objective of the present work is to experimentally and numerically study the effect of the part size on the distortion of a part printed by a powder bed fusion process. A simplified thermo-mechanical finite element model was developed using a so-called superlayer concept (i.e., numerous layers deposited at once) to predict the geometric distortion induced by the thermal stress. A set of seven cylinders with different dimensions were modeled with this method. The same geometries were printed using a commercial selective laser melting machine and cut from the build plate using wire electrical discharge machining. The distortion of different cylinders was measured before and after the removal from the build plate using a coordinate measuring machine and compared with the simulation results. The experimental results showed the final distortion is largely contributed by the build plate removal process because it relaxes the thermal stress accumulated during the printing process. The modeling results show a high consistency with the experimental results, especially for the thicker parts. As the part thickness decreases, the prediction accuracy of the model decreases. When a superlayer thickness of 1 mm is used, the model can accurately predict the distortion for a cylinder with a diameter of 45 mm and a thickness of greater than 6 mm. This model provides an effective approach for geometric control of printed parts.

Additive manufacturing of copper alloys: influence of process parameters and alloying elements

ABSTRACTOwing to the physical properties of copper and its alloys it is challenging to achieve good surface quality and low porosity by the widely used laser-based additive manufacturing processes. This paper deals with the role of alloy composition, powder size and process parameters in additive manufacturing with laser beam melting machine (with power up to 100 W). Test parts were produced in pure copper and CuNiSi(Cr) alloys. The porosity was investigated as a function of different process parameters and powder size ranges. The effects of the alloy physical properties (reflectivity, thermal conductivity, melting range and surface tension) are discussed. Moreover, the effect of thermal treatment on the properties of CuNiSi parts was assessed in conventional two-step heat treatments.

The effect of micro-architecture on the failure response of multi-layered lattice sandwich panels under three-point loading

In this study, the failure behaviour of lattice sandwich panels under three-point loading has been studied using a nonlinear finite element analysis. This paper develops on a previous paper, where the similar failure behaviour was discussed. However, the originality of this paper lies in the fact that it investigates the effect of the micro-architecture of the lattice unit-cell on the failure response of lattice sandwich panels by introducing three geometrical parameters γx, γy and γz. In addition, lattice sandwich panels have been fabricated using a selective laser metal melting machine, and quasi-static bending tests on the panels were conducted and the accuracy of the present method for predicting the failure load is discussed by comparing the experimental data with the analytical results. It has been shown that the analytical results agree reasonably well with the experimental results.

Microstructure and Mechanical Properties of Welded Additively Manufactured Stainless Steels SS316L

Microstructure and mechanical properties of additively manufactured SS316L has been investigated. The samples produced by selective electron beam melting machine were then subjected to gas tungsten arc welding. Various examinations were performed including metallography and microscopy, hardness testing, and tensile testing coupled with digital image correlation software. Strain distribution was clearly evident on the samples during tensile testing with necking taking place at the heat affected zone on both sides of the weldments. From tensile testing, it was clear that the ductility and strengths of the samples were equal to those of conventionally produced samples such as rolled sheet. Hardness testing indicated the uniform distribution across the base metal and the weldments. Scanning electron microscopy identified the presence of Cr and Mo-rich precipitates on the grain boundaries, while the fracture surface was entirely covered with dimples (microvoid coalescence) indicating a ductile fracture mode.

Influence of Selective Laser Melting Machine Source on the Dynamic Properties of AlSi10Mg Alloy.

Selective laser melting (SLM) AlSi10Mg alloy has been thoroughly investigated in terms of its microstructure and quasi-static properties, owing to its broad industrial applications. However, the effects of the SLM process on the dynamic behavior under impact conditions remain to be established. This research deals with the influences of manufacturing process parameters on the dynamic response of the SLM on AlSi10Mg at a high strain rate of 700 to 6700 s−1 by using a split Hopkinson pressure bar apparatus. Examinations were performed on vertically and horizontally built samples, processed individually by two manufacturers using a different laser scanning technique on the same powder composition. It was concluded that the fabrication technique does not influence the true stress–true strain dependency at strain rates of 700 to 2800 s−1. However, at higher strain rates (4000 to 6700 s−1), this study revealed different plastic behavior, which was associated only with the horizontally built samples. Moreover, this study found different failure demeanors at true strains exceeding 0.8. The dynamic response was correlated with the as-built microstructure and crystallographic texture, characterized using the electron backscattered diffraction technique.

Effect of Multi-Elements Substitution on the Mechanical Properties of Intermetallic Compound

It is well known that various elements substitute for a certain sub-lattice of intermetallic compounds. There have been various experimental investigations of the effects of substituted elements on mechanical properties, however, there are few reports describing the effects of multi-element substitution. In the present study, L12-type compounds A3B (Ni3Al and Co3(Al,W)) were selected as model compounds because their substitution behavior is well known. It was reported that various elements such as Ni, Co, Cu, Pd and Pt occupy the A-site, whereas Al, Si, Ga, Ge, Ti, V, Nb, Ta, Mo, and W occupy the B-site. These elements are expected to introduce local lattice distortion, which may affect the motion of dislocations over a wide range of temperatures. Several alloys composed of five or more elements including Ni, Co, Al, Mo, and W, were prepared using an Ar-arc melting machine and heat-treated. Several alloys were found to include an (Ni, Co)3(Al, Mo, W, …)-L12 compound as a constituent phase. The nano-hardness of these L12 phases was higher than that of the high-strength Co3(Al,W)-L12 compound, confirming that multi-element substitution is an effective way to improve the mechanical properties of an intermetallic compound without decreasing the phase stability.

Comparison of different cellular structures for the design of selective laser melting parts through the application of a new lightweight parametric optimisation method

Interest in lightweight geometries and cellular structures has increased due to the freeform capabilities of additive manufacturing technologies. In this paper, six different cellular structures were designed and parameterised with three design variables to carry out the lightweight optimisation of an initial solid sample. According to the limitations of conventional computer-aided design (CAD) software, a new parametric optimisation method was implemented and used to optimise these six types of structures. The best one in terms of optimisation time and stiffness was parameterised with nine design variables, changing the dimensions of the internal cellular structure and the reinforcement zones. These seven optimised geometries were manufactured in a Phenix ProX200 selective laser melting machine without using support. The samples obtained were tested under flexural load. The results show that the cubic cell structures have some advantages in terms of CAD definition, parameterisation and optimisation time because of their simpler geometry. However, from the flexural test results it can be concluded that this type of cell structure and those with horizontal bars experience a loss of stiffness compared to the estimates of the finite element analysis because of imperfections in the manufacturing process of hanging structures.

The Additive Manufacturing Operations Management Maturity: a Closed or an Open Issue?

The term Additive Manufacturing (AM) refers to different kinds of technologies and applications that have in common the ability to build an item starting from a 3D CAD model of the component and by adding materials layer by layer until the product is realised. This paper aims at analysing the existing literature dealing with the use of Metal Additive Manufacturing (MAM) machines for the mass customisation and try to figure out the main issues faced by the international literature about the operations management (OM) issues applied to the MAM. The paper is focusing on several topics such as the technology selection methods, the scheduling and production planning, the spare parts management, the supply chain management and the impact of AM processes on the environmental sustainability of the production systems. The research motivation is also reinforced by the new AM technologies such as Binder Jetting and Direct Energy Deposition (DED) that are promising to ensure deposition rate higher than Selective Laser Melting (SLM) machines and smaller investments